Device for detecting failure of hydraulic motor, and hydraulic vehicle

ABSTRACT

A failure detection device for a hydraulic motor of the present invention comprises a hydraulic pump  3  that is driven by a prime mover  2 ; a hydraulic motor  1  that is driven by hydraulic oil discharged from the hydraulic pump  3 ; an abnormality detection device  35  that detects an abnormal operation of the hydraulic motor  1 ; and a warning device  30, 39, 40  that issues a warning when the abnormal operation of the hydraulic motor  1  is detected by the abnormality detection device  35.

TECHNICAL FIELD

[0001] This invention relates to a device that detects a failure of thehydraulic motor installed in the hydraulic drive vehicle such as awheeled hydraulic excavator.

BACKGROUND ART

[0002] Generally, the hydraulic drive vehicle such as a wheeledhydraulic excavator comprises a hydraulic pump and a hydraulic motor fortravelling which is driven by oil discharged from the hydraulic pump.The output shaft of this hydraulic motor is connected with the inputshaft of the transmission, and the rotation of the hydraulic motor istransmitted to the wheels through the transmission. A drain chamber isprovided to the hydraulic motor, and the drain oil from the hydraulicmotor returns to a reservoir via the drain chamber.

[0003] In such a hydraulic drive vehicle as described above, if aforeign body should be ingested by the hydraulic motor, proper operationof the hydraulic motor is impeded and there is a danger that thehydraulic motor may be damaged. If the hydraulic motor is damaged, thedischarged oil from the hydraulic pump flows into the drain chamber andin some cases it may flow into the transmission. As a result, thetransmission therein is filled with the oil, and a great resistancecomes to act on the transmission so that the travelling performance ofthe vehicle deteriorates. Moreover, when transmission oil becomes mixedwith the oil from the hydraulic motor, the quality of the mission oilmay be deteriorated, and this may exert a negative influence upon theoperation of the transmission.

DISCLOSURE OF THE INVENTION

[0004] An object of the present invention is to provide a failuredetection device for a hydraulic motor that is capable of detecting anabnormality of the hydraulic motor and responding appropriately to theabnormal operational situation.

[0005] Moreover, another object of the present invention is to provide ahydraulic drive vehicle which is equipped with such a failure detectiondevice for a hydraulic motor.

[0006] In order to achieve the object described above, a failuredetection device for a hydraulic motor according to the presentinvention comprises a hydraulic pump that is driven by a prime mover; ahydraulic motor that is driven by hydraulic oil discharged from thehydraulic pump; an abnormality detection device that detects an abnormaloperation of the hydraulic motor; and a warning device that issues awarning when the abnormal operation of the hydraulic motor is detectedby the abnormality detection device.

[0007] Furthermore, a hydraulic drive vehicle according to the presentinvention comprises a hydraulic pump that is driven by a prime mover;ahydraulicmotor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; an abnormality detection device that detects anabnormal operation of the hydraulic motor for traveling; and a warningdevice that issues a warning when the abnormal operation of thehydraulic motor for traveling is detected by the abnormality detectiondevice.

[0008] Therefore, it is possible for an operator to recognize anyabnormal operation of the hydraulic motor at an early stage and to takemeasures appropriate to such abnormal operation.

[0009] A driving of the hydraulic motor may be restricted instead ofissuing the warning.

[0010] The hydraulic motor may be a hydraulic motor for traveling and itis desirable to lower a rotational speed of the prime mover when theabnormal operation of the hydraulic motor for traveling is detected. Itis also acceptable to stop traveling and moreover to apply a brake afterthe traveling has stopped. It is preferable to prevent a restarting ofthe prime mover when the abnormal operation of the hydraulic motor fortraveling is detected. In addition, the warning may be issued.

[0011] The abnormal operation of the hydraulic motor can be detectedaccording to increase of a drain pressure of the hydraulic motor ordeterioration of a seal member that prevents a drain oil of thehydraulic motor from flowing out.

[0012] The operation of the warning device and the drive restrictionupon the vehicle may be disabled when the working state has beendetected.

[0013] It is preferable to reset the above-described control accordingto a reset command. The reset command may be issued in response toactuation of an ignition key switch.

BRIEF DECSRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the first embodiment of the presentinvention.

[0015]FIG. 2 is sectional view of a traveling motor to which the presentinvention has been applied.

[0016]FIG. 3 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the firstembodiment of the present invention.

[0017]FIG. 4 is a flow chart showing an example of procedure executed bythe controller.

[0018]FIG. 5 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for thehydraulic motor according to the second embodiment of the presentinvention.

[0019]FIG. 6 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the secondembodiment of the present invention.

[0020]FIG. 7 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the third embodiment of the presentinvention.

[0021]FIG. 8 schematically illustrates the details of the controllerwhich constitutes the failure detection device according to the thirdembodiment of the present invention.

[0022]FIG. 9 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the fourth embodiment of the presentinvention.

[0023]FIG. 10 schematically illustrates the details of the controllerwhich constitutes the failure detection device according to the fourthembodiment of the present invention.

[0024]FIG. 11 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the fifth embodiment of the presentinvention.

[0025]FIG. 12 schematically illustrates the details of the controllerwhich constitutes the failure detection device according to the fifthembodiment of the present invention.

[0026]FIG. 13 shows a modification example of the failure detectiondevice according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] First Embodiment

[0028] A wheeled hydraulic excavator that is equipped with a failuredetection device according to the first embodiment of the presentinvention will now be described with reference to FIGS. 1 through 4. Thewheeled hydraulic excavator comprises a wheeled undercarriage upon whichan upper-structure is rotatably mounted, and a working attachment isfitted to this upper-structure. A hydraulic motor 1 for traveling whichis driven by a hydraulic circuit for traveling shown in the FIG. 1 isprovided in the undercarriage.

[0029] As shown in FIG. 1, hydraulic oil is discharged from a main pump3 which is driven by an engine, the direction and flow rate of thedischarged oil are controlled by a control valve 4, and then thehydraulic oil is supplied to a traveling motor 1 via a brake valve 6with a built-in counterbalance valve 5. A transmission 7 is connectedwith an output shaft 1 a of the traveling motor 1. The rotational speedof the traveling motor 1 is changed by the transmission 7, and therotational output is transmitted to tires 10 through propeller shafts 8and axles 9. Thus, the wheeled hydraulic excavator is propelled. Itshould be noted that the pressure oil from the main pump 3 is alsosupplied to a hydraulic circuit for working which is not shown in thefigure, and drives actuators for working.

[0030] The direction of changeover and operation amount of the controlvalve 4 are controlled by pilot pressure from a pilot control circuit.The traveling speed of the vehicle can be controlled by controlling theamount by which the control valve 4 is operated. The pilot controlcircuit comprises a pilot pump 21, a traveling pilot valve 23 thatgenerates a secondary pilot pressure P1 according to the amount by whichan accelerator pedal 22 is stepped upon, a slow-return valve 24 thatdelays oil returning to the pilot valve 23, and a forward/reverseswitchover valve 25 which is used for selecting forward traveling,reverse traveling or neutral for the vehicle. The forward/reverseswitchover valve 25 is constituted of a solenoid-controlled directionalcontrol valve, and its position is changed over by operating a switchnot shown in the figures.

[0031]FIG. 1 shows the situation with the forward/reverse switchovervalve 25 in its neutral (N) position, and moreover when the travelingpilot valve 23 is not being operated. Accordingly, the control valve 4is in its neutral position, the pressure oil from the main pump 3returns to a reservoir, and the vehicle remains stopped. When theforward/reverse switchover valve 25 is switched to its forward travelingposition (F position) or to its reverse traveling position (R position)by the operation of the switch, and then the accelerator pedal 22 isstepped upon, the secondary pressure according to the amount by whichthe accelerator pedal is operated acts on a pilot port of the controlvalve 4. The control valve 4 is operated by the operation amountcorresponding to the secondary pilot pressure P1. Thus, the dischargedoil from the main pump 3 is led to the traveling motor 1 via the controlvalve 4, a center joint 12 and the brake valve 6, so as to drive thetraveling motor 1. At this time, the leakage oil from the travelingmotor 1 is collected to the reservoir through a drain line (drainchamber) 11.

[0032] When the accelerator pedal 22 is released during vehicletraveling, the pressure oil from the pilot pump 21 is interrupted by thetraveling pilot valve 23, and an outlet port of the traveling valve isconnected to the reservoir. As a result, the pressure oil having actedon the pilot port of control valve 4 returns to the reservoir via theforward/backward switchover valve 25, the slow-return valve 24 and thetraveling pilot valve 23. At this time, the returning oil flow isrestricted by the restriction of the slow-return valve 24, so that thecontrol valve 4 returns to its neutral position gradually. When thecontrol valve 4 returns to its neutral position, the supply of thepressure oil (drive pressure) is interrupted, and the counterbalancevalve 5 is then switched to its neutral position as shown in FIG. 1.

[0033] At this time, the vehicle continues to progress due to itsinertia force, and the operation of the traveling motor 1 changes overfrom motor action to pump action, in which its B port is its suction(inlet) port and its A port is its discharge (outlet) port in FIG. 1.Flow of the pressure oil from the traveling motor 1 is restricted by therestriction of the counterbalance valve (neutral restriction), thepressure between the counterbalance valve 5 and the traveling motor 1then rises and acts on the traveling motor 1 as brake pressure. As aresult, the traveling motor 1 generates the brake torque to slow thevehicle down. If, during the pump operation of the hydraulic motor, thequantity of oil flowing into the traveling motor 1 becomes insufficient,the additional oil is supplied from a make-up port 13 thereto. Themaximum brake pressure is regulated by relief valves 14 and 15.

[0034] A governor 2 a of the engine 2 is connected with a pulse motor 32via a link mechanism 31, and the rotational speed of engine 2 iscontrolled by rotation of the pulse motor 32. In particular, the enginespeed is increased by the normal rotation of the pulse motor 32, whileit is decreased by the reverse rotation of the pulse motor. Apotentiometer 33 is connected with the governor 2 a via the linkmechanism 31, and the potentiometer 33 detects a governor lever anglecorresponding to the rotational speed of the engine 2. The detectedvalue is input to the controller 30 as a control rotational speed Nθ.

[0035] Furthermore, the controller 30 is connected with a pressuresensor 34 that detects the secondary pilot pressure P1 generated by thetraveling pilot valve 23, corresponding to the pedal operation amount, apressure sensor 35 that detects the pressure (drain pressure P2) of theleakage oil from the traveling motor 1, a reset switch 36, and anignition key switch 37 that is turned on/off according to the operationof an ignition key, respectively. A power source 38 is connected withthe key switch 37, and the electrical power is supplied to thecontroller 30 in response to the key switch 37 being turned on.Accordingly, the controller 30 implements calculations as will bedescribed later, to control the rotation of the pulse motor 32 byoutputting the control signal to the pulse motor 32 and also to controloperations of a buzzer 39 and a warning lamp 40 by outputting controlsignals thereto.

[0036] Next, the construction of the traveling motor 1 will beexplained. FIG. 2 is a sectional view of the variable displacementtraveling motor 1. As shown in FIG. 2, a plurality of pistons 42 (onlyone of which is shown in the figure) are connected with a flange 41 ofthe output shaft 1 a of the traveling motor 1, along its circumference.The pistons 42 are slidably inserted into oil chambers 43 a formed in acylinder block 43 through piston rings 42 a. The end of the cylinderblock 43 comes into contact with a swash plate 44, and their contactingsurfaces mutually define a circular cone shape. The swash plate 44 canbe swung or inclined together with the cylinder block 43 in thedirection of the arrow shown in the figure, and the motor displacementvaries according to the swing amount or inclined angle of the swashplate.

[0037] An inlet or suction port and an outlet or delivery port of oil,not shown in the figure, are provided in the swash plate and a motorcover 45 which is in contact with the swash plate 44, the suction portand the delivery port extending over half a phase of the motor rotation,respectively. And, the pressure oil from main pump 3 flows into the oilchambers 43 a through the suction port, while the oil from the oilchambers 43 a flows out to the reservoir through the delivery port. Dueto this, the pistons 42 are slid within the oil chambers 43 a, and,while the swash plate 44 is kept incontact with the cylinder block 43,the output shaft 1 a of the motor 1 rotates as a unit with the cylinderblock 43 and the pistons 42. An input shaft 7 a of the transmission 7 isconnected by splines with the motor output shaft 1 a so that therotation of the traveling motor 1 is transmitted to the transmission 7.

[0038] At this time, portions of the pressure oil which is supplied tothe oil chambers 43 a from the main pump 3 leaks into the drain chamber11 through gaps between the mutually contacting surfaces of the swashplate 44 and the cylinder block 43, or gaps between the mutually slidingsurfaces of the pistons 42 and the oil chambers 43 a. The leakage oil isreturned to the reservoir through a drain hole 11 a which is formed atthe bottom of motor casing 46.

[0039] If, at this time, a foreign body, for example, should get intothe mutually sliding surfaces of one of the pistons 42 and causes thepiston 42 to stick in (to contact directly with) the cylinder block 43,the cylinder block 43 rotates while being dragged by the piston 42 andthen, the gap between the cylinder block 43 and the swash plate 44becomes partially increased. Moreover, according to circumstances, thepiston ring 42 a may be damaged, which causes the gap between themutually sliding surfaces to become wider. As a result, a large quantityof the pressure oil from the main pump 3 flows into the drain chamber 11through these gaps, and the oil pressure in the drain chamber 11 mayincrease. And, the oil from the drain chamber 11 may flow into thetransmission 7 through and past seal rings SR.

[0040] In this embodiment, this type of abnormal operation of thetraveling motor 1 is detected with the pressure sensor 35, and thefollowing countermeasure takes place for such abnormal state.

[0041]FIG. 3 is a schematic illustration to explain details of thecontroller 30. When the ignition key switch 37 is turned on, theelectric power is supplied to the controller 30 to start execution ofits processing. A function generator 301 outputs a set signal to a setterminal S of RS flip-flop 302 when the motor drain pressure which havebeen detected by the pressure sensor 35 is greater than or equal to thepredetermined value P2a which is set in advance. Here, the predeterminedvalue P2a is set to represent the oil pressure in the drain chamber 11in the case of failure of the traveling motor 1 as described above. Whenthe detected pressure value P2 reaches the predetermined value P2a orover, it may be determined that the traveling motor 1 has broken down.When the set signal is input to the set terminal S of the flip-flop 302,the flip-flop 302 outputs a high-level signal from its terminal Q tochange over a switchover circuit 303 to its contact “a” side. As aresult, electrical power is supplied to a buzzer 39 and a warning lamp40, so that the buzzer emits sound and the buzzer lamp 40 isilluminated.

[0042] When a reset switch 36 is turned on, the reset switch 36 outputsa reset signal to a reset terminal R of the flip-flop 302. The flip-flop302 sets low-level in the terminal Q in response to this reset signal,and the switchover circuit 303 is then switched to its contact “b” side.As a result, the supply of electrical power to the buzzer 39 and thewarning lamp 40 is interrupted so that the buzzer sound is brought to ahalt and the warning lamp 40 is extinguished.

[0043] A function by which the engine speed should increase along withincrease of the traveling pilot pressure is set in advance in thefunction generator 304, as schematically shown in the figure. Thefunction generator 304 sets the rotational speed N corresponding to thedetected value P1 from the pressure sensor 34 based upon this function,and outputs this set value N to a switchover circuit 305. The switchovercircuit 305 is changed over according to change of the switchovercircuit 303. That is, when the switchover circuit 303 is switched to itscontact “a” side, the switchover circuit 305 is also switched to itscontact “a” side, and when the switchover circuit 303 is switched to itscontact “b” side, the switchover circuit 305 is also switched to itscontact “b” side. Accordingly, the switchover circuit 305 selects eitherthe rotational speed N as set by the function generator 304 or an idlingrotational speed Ni which is set in advance in a rotational speedsetting device 306, and outputs its selected rotational speed to a servocontrol section 307 as a target rotational speed Ny. In the servocontrol section 307, the target rotational speedNyis comparedwith thecontrol rotational speed Nθ which corresponds to the amount ofdisplacement of the governor lever as detected by the potentiometer 33,and the pulse motor 32 is controlled so as to bring the controlrotational speed NO to match the target rotational speed Ny, accordingto the procedure shown in FIG. 4.

[0044] Referring to FIG. 4, first in step S21, the rotational speedcommand value Ny and the control rotational speed Nθ are read in, andthen the flow of control proceeds to step S22. In step S22, Ny issubtracted from Nθ and the result of this subtraction, i.e. therotational speed differential A, is stored in a memory. In step S23,using a predetermined standard rotational speed differential K, it makesa decision as to whether or not |A|≧K. If an affirmative decision ismade, the flow of control proceeds to step S24 in which a decision ismade as to whether or not the rotational speed differential A>0. If A>0,it implies that the control rotational speed Nθ is greater than therotational speed command value Ny, in other words, the controlrotational speed is higher than the target rotational speed, the flow ofcontrol then proceeds to step S25 in which a signal for instructingreverse rotation of the motor is output to the pulse motor 32 in orderto reduce the engine speed. As a result, the pulse motor 32 is caused torotate in reverse so that the rotational speed of the engine 2 drops.

[0045] On the other hand, if A≦0, it implies that the control rotationalspeed Nθ is lower than the rotational speed command value Ny, that is,the control rotational speed is lower than the target rotational value,a signal for instructing normal rotation of the motor is output in orderto increase the engine speed, in step S26. As a result, the pulse motor32 performs normal rotation to increase the engine speed. If a negativedecision is made in step S23, the flow of control proceeds to step S27to output a motor stop signal. Therefore, the rotational speed of theengine 2 is maintained constant. After the appropriate one of the stepsS25-S27 has been executed, the flow of control returns to the beginningof this flow chart.

[0046] The outstanding features of the operation of this failuredetection device for a hydraulic drive vehicle constructed as describedabove will now be explained in concrete term.

[0047] (1) During Normal Operation of the Traveling Motor

[0048] When the traveling motor 1 is in the normal operating condition,the leakage oil hardly flows out from the traveling motor 1 so that theoil pressure in the drain chamber 11 remains equal to or less than thepredetermined value P2a. Accordingly, the switchover circuit 303 and theswitchover circuit 305 of the controller 30 are switched to theircontact “b” side, respectively. Due to this, the buzzer 39 and thewarning lamp 40 stop their operation. In this condition, if theforward/backward switchover valve 25 is switched to forward traveling orto reverse traveling, and also the accelerator pedal 22 is stepped upon,the traveling pilot pressure P1 is generated in correspondence to theamount by which the accelerator pedal is operated. The servo controlsection 307 compares the target rotational speed Ny according to thistraveling pilot pressure P1 with the control rotational speed Nθcorresponding to the detected value from the potentiometer 33, and thencontrols the pulse motor 32 to bring both rotational speeds tocorrespond to each other. Therefore, the engine speed increases in linewith the increase of the amount of pedal operation.

[0049] (2) When Operation of the Traveling Motor Becomes Abnormal

[0050] If the motor piston 42 should get stuck at its sliding portioncaused by a foreign body having gotten into the sliding portion, a largequantity of delivery oil from the hydraulic pump 3 may flow into thedrain chamber 11 resulting in increase of the pressure in the drainchamber 11, as described above. And, when the drain pressure reaches thepredetermined value P2a, the function generator 301 outputs the setsignal to the set terminal of the flip-flop 302 so that the switchovercircuit 303 is switched to its contact “a” side in response to a highlevel signal output from the Q terminal of the flip-flop 302. As aresult, the buzzer sound is generated and the warning lamp 40 isilluminated so that an operator is able to recognize the abnormal stateof the traveling motor 1. As a result, it is possible for the operatorto respond appropriately to such abnormal circumstances, for instance byoperating a brake.

[0051] The switchover circuit 305 is also switched to the contact “a”side according to changeover of the switchover circuit 303. Due to this,the engine speed is lowered to its idling rotational speed Ni regardlessof an amount of the pedal actuation, and the motor rotational speed alsodrops in line with reduction in amount of the delivery oil from thepump. As a result, the quantity of oil flow into the drain chamber 11decreases, so that it is possible to reliably prevent negative influence(secondary damage), such as the oil leakage from the drain chamber 11into the transmission 1, that may be caused due to the abnormality ofthe traveling motor 1. Moreover, because the vehicle is decelerated, itis possible to stop the vehicle promptly by the brake operation. Uselessconsumption of fuel can be prevented as well.

[0052] In the state in which the motor drain pressure becomes equal toor below the predetermined value P2a after the traveling motor 1 hasstopped, when the reset switch 36 is operated, the terminal Q of theflip-flop 302 is set to low level so that the switchover circuit 303 isswitched to the contact “b” side and then the switchover circuit 305 isalso switched to the contact “b” side. Due to this, the buzzer sound isstopped and also the warning lamp 40 is extinguished. In other words,the operator can intentionally stop the operation of the warningdevices. Moreover, it becomes again possible to control the engine speedin accordance with operation of the accelerator pedal. As a result, whenthe vehicle is to be transported upon a trailer for the repair of thetraveling motor 1, it is possible to load the vehicle onto the trailerby driving it under its own power. It should be understood that, insteadof operating the reset switch 36, it would also be acceptable to turnoff the ignition key switch 37. If the traveling motor 1 is damagedheavily and driving the vehicle under its own power is difficult orimpossible, it may be pulled up on the trailer by engaging the end of abucket of the hydraulic excavator with part of the trailer and thenactuating hydraulic cylinders for a boom or arm.

[0053] According to the first embodiment as described above, when thebreakdown of the traveling motor 1 is detected based upon the increasein the motor drain pressure, warning, such as buzzer sounds andillumination of the warning lamp 40 is issued. Therefore, it is possiblefor an operator to be made aware of abnormal operation of the travelingmotor 1 at an early stage, and to respond appropriately to such abnormalcircumstances. Moreover, the engine speed is lowered to the idlingrotation speed Ni to restrict the drive of the traveling motor 1 when abreakdown of the motor 1 is detected. As a result, the quantity of oilflowing into the drain chamber 11 decreases, so that it becomes possibleto prevent the secondary damage that may be caused by the failure of thetraveling motor 1. Since the engine speed is lowered to the idlingrotational speed so that the vehicle is slowed down and travels at verylow speed, it is possible to pull the vehicle slowly to the shoulder ofthe road and to stop. Moreover, a useless waste of fuel can beprevented. In addition, the warning is kept issued and restriction uponthe traveling of the vehicle is maintained until the reset switch 36 isoperated or alternatively the ignition key switch 37 is turned off.Therefore, an operator is able to recognize the abnormal state of thetraveling motor 1. In the state in which the drain pressure is equal toor below the predetermined value P2a, when the reset switch 36 isoperated or the ignition key switch 36 is turned off alternatively, theengine speed can again be increased according to the operation of theaccelerator pedal and it is possible to load the vehicle upon thetrailer or the like easily.

[0054] Second Embodiment

[0055] In the first embodiment, the engine speed is lowered to theidling rotational speed Ni to decelerate the vehicle during a failure ofthe traveling motor 1. The vehicle traveling will be stopped in thesecond embodiment. The second embodiment of the present invention willnow be explained with reference to FIGS. 5 and 6. FIG. 5 is a circuitdiagram showing the structure of a wheeled hydraulic excavator which isequipped with a failure detection device according to the secondembodiment, and FIG. 6 schematically illustrates details of a controller30A according to the second embodiment. It should be noted that the samereference numerals are used for elements identical to that of FIGS. 1and 3, and the explanations will focus on the points differenttherefrom.

[0056] As shown in FIG. 5, the line between the traveling pilot valve 23and the slow-return valve 24 can be connected with the reservoir througha solenoid valve 47. The solenoid valve 47 is controlled by a controlsignal from the controller 30A. A solenoid 47 a of the solenoid valve 47is connected with the switchover circuit 303 as shown in FIG. 6. Whenthe pressure in the drain chamber 11 rises to the predetermined valueP2a and the switchover circuit 303 is switched to the contact “a” side,the solenoid 47 a is excited to switch the solenoid valve 47 to itsposition B. The pressure oil having acted on the pilot port of controlvalve 4 returns to the reservoir via the forward/backward switchovervalve 25, the slow-return valve 24 and the solenoid valve 47, and thecontrol valve 4 is driven back to its neutral position. As a result, thesupply of pressure oil to the traveling motor 1 is intercepted, and thevehicle stops traveling regardless of an actuation amount of theaccelerator pedal. In addition, the warning devices start theiroperation, and the engine speed is limited to the idling rotationalspeed Ni. It would also be acceptable to control the engine speedaccording to the value corresponding to the traveling pilot pressureinstead of limiting the engine speed to the idling rotational speed Ni.In this case, the switchover circuit 305 would become unnecessary.

[0057] If the reset switch 36 is actuated while the solenoid 47 a isexcited, the switchover circuits 303 and 305 are switched to the contact“b” side, respectively. Accordingly, the solenoid 47 a is demagnetized,and the solenoid valve 47 is switched to its position A. As a result,the traveling pilot pressure corresponding to the operation of theaccelerator pedal is made to act on the pilot port of the control valve4, and the supply of the pressure oil to the traveling motor 1 becomespossible.

[0058] According to the second embodiment as described above, when afailure of the traveling motor 1 is detected, the traveling pilotpressure is made to return to the reservoir by the operation of thesolenoid valve 47. Therefore, it is possible immediately to stop thevehicle from traveling without performing brake operation and to respondappropriately to the abnormality of the traveling motor 1.

[0059] Third Embodiment

[0060] In the second embodiment, the vehicle traveling is stopped duringa failure in the traveling motor 1. A brake (a parking brake) isadditionally applied to the vehicle in the third embodiment. The thirdembodiment of the present invention will now be explained with referenceto FIGS. 7 and 8. FIG. 7 is a circuit diagram showing the constructionof a wheeled hydraulic excavator which is equipped with a failuredetection device according to the third embodiment, and FIG. 8schematically illustrates the structure of a controller 30B according tothe third embodiment. It should be noted that the same referencenumerals are used for elements identical to that of FIGS. 5 and 6, andthe explanation will focus on the points different therefrom.

[0061] As shown in FIG. 7, a vehicle speed sensor 48 that detects atraveling speed of the vehicle and a solenoid valve 49 for operating theparking brake are additionally provided. It should be noted that theparking brake is of type that is well-known and is operated according toopen/close operation of the solenoid valve 49, and a drawing of which isomitted herein. As shown in FIG. 8, a solenoid 49 a of the solenoidvalve 49 is connected with the switchover circuit 303 via a switchovercircuit 308. A function generator 309 switches the switchover circuit308 according to a detection value V from the vehicle speed sensor 48.

[0062] When the vehicle traveling, the function generator 309 switchesthe switchover circuit 308 to the contact “b” side as shown in thefigure. As a result, the solenoid 49 a is demagnetized to release theparking brake. When the switchover circuit 303 is switched to thecontact “a” side due to a failure of the traveling motor 1, the solenoid47 a of the solenoid valve 47 is excited to stop the vehicle asdescribed above. After that, when it is detected by the vehicle speedsensor 48 that the vehicle has stopped, in other words the vehicle speedbecomes zero, the function generator 309 switches the switchover circuit308 to the contact “a” side. As a result, the solenoid 49 a is excitedto engage the parking brake in operation. When the switchover circuit303 is switched to the contact “b” side according to the reset switchturned on, the solenoid 49 a is demagnetized and accordingly the parkingbrake is released. It should be noted that the engine speed may be ormay not be restricted to the idling rotational speed in the case of afailure of the traveling motor 1 in the third embodiment. Moreover, atimer may be connected with the function generator 309 to detect thatthe state in which the vehicle speed is zero is maintained for apredetermined time period. In this case, the switchover circuit 308 isswitched to the contact “a” side when the predetermined time period haselapsed after the vehicle speed becomes zero.

[0063] According to the third embodiment, when stopping of the travelingmotor 1 due to a failure of the traveling motor 1 is detected, theparking brake is additionally applied. In this manner, it would bepossible to ensure the stationary state of the vehicle even when it ison the slope.

[0064] Fourth Embodiment

[0065] In the second embodiment, the vehicle traveling is stopped duringa failure of the motor. In addition to this function, the engine 2 isprohibited from restarting in the fourth embodiment. The fourthembodiment of the present invention will now be explained with referenceto FIGS. 9 and 10. FIG. 9 is a circuit diagram showing the structure ofa wheeled hydraulic excavator equipped with a failure detection deviceaccording to the fourth embodiment, and FIG. 10 schematicallyillustrates details of a controller 30C according to the fourthembodiment. It should be noted that the same reference numerals are usedfor elements identical to that of FIGS. 5 and 6, and the explanationwill focus on the points different therefrom.

[0066] As shown in FIG. 9, a starting motor 51 is connected with thecontroller 30C, and the drive of the starting motor 51 is controlledthereby. As shown in FIG. 10, the ignition key switch 37 is connectedwith the starting motor 51 via a relay 310, and the output terminal ofthe switchover circuit 303 is connected with the coil of the relay 310.By this structure, when the switchover circuit 303 is switched to thecontact “a” side according to a failure of the traveling motor 1, thesolenoid 47 a is excited to stop the vehicle traveling. And the coil ofthe relay 310 is supplied with actuating electrical energy so that therelay contact is switched to its contact “R2” side. As a result, thesupply of electricity to the starting motor 51 is cut, and it isimpossible to start the engine 2 even if the ignition key switch 37 isturned on.

[0067] When, in such a state, the reset switch 36 is actuated, theswitchover circuit 303 is switched to the contact “b” side, and thesupply of electricity to the coil of the relay 310 is intercepted. Therelay contact is thus switched to the contact “R1” side, which makespossible to restart the engine 2. It should be noted that it would alsobe possible to restart the engine 2, as an alternative to operation ofthe reset switch 36, by a repairman, etc. using some apparatuses tosupply an external signal of some type. In this manner, it would not bepossible for an operator to restart the engine upon his own decision.While, in the fourth embodiment, the vehicle is made to stop travelingduring a failure of the traveling motor 1, it is also acceptable tolimit the engine speed or to apply the parking brake as alternatives.

[0068] According to the fourth embodiment as described above, the engineis prohibited from restarting when a failure of the traveling motor 1 isdetected. Therefore, an operator will not imprudently restart the engine2 to drive the vehicle, and it is possible to ensure that he makes anappropriate response to the abnormal operation of the traveling motor 1.

[0069] Fifth Embodiment

[0070] In the first embodiment, the engine speed is limited to theidling rotational speed when a failure of the traveling motor 1 isdetected, regardless of the traveling state or the working state. In thefifth embodiment, the engine speed is limited only during the travelingstate. The fifth embodiment of the present invention will now beexplained with reference to FIGS. 11 and 12. FIG. 11 is a circuitdiagram showing the structure of a wheeled hydraulic excavator equippedwith a failure detection device according to the fifth embodiment, andFIG. 12 schematically illustrates details of a controller 30D accordingto the fifth embodiment. It should be noted that the same referencenumerals are used for elements identical to that of FIGS. 1 and 3, andthe explanations will focus on the points different therefrom.

[0071] As shown in FIG. 11, a forward/reverse changing switch 52 foroutputting a switching command to the forward/reverse switchover valve25, and a brake switch 53 for outputting an operate command to a workbrake not shown in the figures are also connected to the controller 30D.As shown in FIG. 12, a switchover circuit 311 is connected with theterminal Q of the flip-flop 302, and the switchover circuit 311 isswitched according to a signal from a work detection section 312.Signals from the forward/reverse changing switch 52 and the brake switch53 are inputted to the work detection section 312. The work detectionsection 312 sets the switchover circuit 311 to the contact “a” side whenthe forward/reverse switchover valve 25 is in the neutral position andalso the work brake is being operated, while in other conditions, theswitchover circuit 311 is switched to the contact “b” side.

[0072] Accordingly, the switchover circuit 311 is switched to thecontact “b” side during the vehicle traveling. And in this condition ifa failure of the traveling motor 1 occurs the switchover circuits 303and 305 are switched to the contact “a” side to restrict the enginespeed to the idling rotational speed Ni. When, in such a condition, theforward/reverse switchover valve 25 is set to the neutral position inresponse to the operation of the forward/reverse changing switch 52, andalso the work brake is operated by the operation of the brake switch 53,the switchover circuit 311 is then switched to the contact “a” side. Inresponse to such changeover, the switchover circuits 303 and 305 areboth switched to the contact “b” side to cancel the restriction of theengine speed. As a result, it is possible to again increase the enginespeed according to the pedal actuation and to continue working in thenormal manner. In this condition, if the forward/backward switchovervalve 25 is switched to forward traveling or to reverse traveling,intending to travel the vehicle, the switchover circuits 303 and 305 areboth switchedto the contact “a” side. As a result, the engine speed ismade to decrease to the idling rotational speed Ni again.

[0073] According to the fifth embodiment, it is decided as to whether ornot the work operation has started according to actuations of theforward/reverse changing switch 52 and the brake switch 53, and therestriction of the engine speed is disabled during the work operation.Therefore, it is possible to continue working in the normal manner evenwhen the traveling motor 1 has broken down. It should be noted that thefifth embodiment can be applied, not only to a system which restrictsthe engine speed during a failure of the traveling motor 1, but also, inthe same manner, to systems which controls the vehicle traveling inother ways, such as by stopping the vehicle traveling, by preventing theengine from restarting, or by causing the parking brake to operate.

[0074] While the pressure rise in the drain chamber 11 is detected bythe pressure sensor 35 to detect the failure of the traveling motor 1 asdescribed above, the failure of the traveling motor 1 may be detected inother ways. By way of example, a sensor (a pressure sensor) 100 fordetecting oil leakage from the drain chamber 11 into the transmission 7may be provided at a portion of seal section of the motor output shaft 1a. And, it may be determined that the traveling motor 1 has broken downwhen the sensor 100 detects the oil leakage caused by damages upon theseal rings SR. It is also acceptable to detect oil level in thetransmission 7 instead of using the sensor 100. In this case, thefailure of the traveling motor 1 may be determined when the oil level inthe transmission 7 is increased by oil flowing from the drain chamber11. In addition, a sensor (G sensor or the like) for the impactdetection may be installed, for example at a bearing that holds themotor output shaft 1 a, and when this sensor detects the impact loadwhich is greater than or equal to a predetermined value, it shall bedetected that the traveling motor 1 has broken down.

[0075] Moreover, although in the above described embodiments, the buzzersound is emitted along with the illumination of the warning lamp 40 whenthe traveling motor 1 has broken down, it would also be acceptable toprovide one of the warning devices. Furthermore, it would be possible toflash the hazard warning lamps which are provided around the vehicle, inorder to arouse the attention around the vehicle. Although, upon afailure of the traveling motor 1, the provision of warning and therestriction of the vehicle traveling have been performed at the sametime, it would be also acceptable to perform only one of them. Moreover,although the driving of the traveling motor 1 is limited during afailure of the traveling motor 1, driving of other actuators, such as aswing motor, may as well be restricted. Finally, in the above describedembodiments, the abnormality of the traveling motor 1 is detected usingthe pressure sensor 35 or the like, the abnormal state of otherhydraulic motors may be detected.

INDUSTRIAL APPLICABILITY

[0076] While a failure detection device for a hydraulic motor has beenexplained in terms of application to a wheeled hydraulic excavator byway of example, it would also be possible, in the same manner, to applythe failure detection device of the hydraulic motor according to thepresent invention to a crawler hydraulic excavator, or to other kinds ofhydraulic drive vehicles.

1. A failure detection device for a hydraulic motor, comprising: ahydraulic pump that is driven by a prime mover; a hydraulic motor thatis driven by hydraulic oil discharged from the hydraulic pump; anabnormality detection device that detects an abnormal operation of thehydraulic motor; and a warning device that issues a warning when theabnormal operation of the hydraulicmotor is detected by the abnormalitydetection device.
 2. A failure detection device for a hydraulic motor,comprising: a hydraulic pump that is driven by a prime mover; ahydraulic motor that is driven by hydraulic oil discharged from thehydraulic pump; an abnormality detection device that detects an abnormaloperation of the hydraulic motor; and a drive restriction device thatrestricts a driving of the hydraulic motor when the abnormal operationof the hydraulic motor is detected by the abnormality detection device.3. A failure detection device for a hydraulic motor according to claim2, wherein: the hydraulic motor is a hydraulic motor for traveling.
 4. Afailure detection device for a hydraulic motor according to claim 3,wherein: the drive restriction device is a rotational speed restrictiondevice that restricts a rotational speed of the primemover, andtherotationalspeedrestrictiondevicelowers the rotational speed of theprime mover to a predetermined rotational speed when the abnormaloperation of the hydraulic motor for traveling is detected by theabnormality detection device.
 5. A failure detection device for ahydraulic motor according to claim 3, wherein: the drive restrictiondevice is a traveling prevention device that prevents the driving of thehydraulic motor for traveling, and the traveling prevention deviceprevents the hydraulic motor for traveling from being driven when theabnormal operation of the hydraulic motor for traveling is detected bythe abnormality detection device.
 6. A failure detection device for ahydraulic motor according to claim 3, further comprising: a stoppingdetection device that detects whether the hydraulic motor for travelinghas stopped; and a brake device that applies a brake upon the hydraulicmotor for traveling when the abnormality detection device detects theabnormal operation of the hydraulic motor for traveling and moreover thestopping device detects that the hydraulic motor for traveling hasstopped.
 7. A failure detection device for a hydraulic motor accordingto claim 3, further comprising: a restart prevention device thatprevents a restarting of theprime mover when the abnormal operation ofthe hydraulic motor for traveling is detected by the abnormalitydetection device.
 8. A failure detection device for a hydraulic motoraccording to claim 2, further comprising: a warning device that issues awarning when the abnormal operation of the hydraulic motor is detectedby the abnormality detection device.
 9. A failure detection device for ahydraulic motor according to claim 1, wherein: the abnormality detectiondevice detects the abnormal operation of the hydraulic motor based upona drain pressure of the hydraulic motor.
 10. A failure detection devicefor a hydraulic motor according to claim 2, wherein: the abnormalitydetection device detects the abnormal operation of the hydraulic motorbased upon a drain pressure of the hydraulic motor.
 11. A failuredetection device for a hydraulic motor according to claim 1, furthercomprising: a seal member that prevents a drain oil of the hydraulicmotor from flowing out of the hydraulic motor, wherein the abnormalitydetection device detects the drain oil which flows out due to a damageupon the seal member.
 12. A failure detection device for a hydraulicmotor according to claim 2, wherein: a seal member that prevents a drainoil of the hydraulic motor from flowing out of the hydraulic motor,wherein the abnormality detection device detects the drain oil whichflows out due to a damage upon the seal member.
 13. A failure detectiondevice for a hydraulic motor according to claim 1, further comprising: aworking detection device that detects a working state, and a warningcontrol device that disables the warning device from issuing the warningwhen the working detection device detects the working state.
 14. Afailure detection device for a hydraulic motor according to claim 2,further comprising: a working detection device that detects a workingstate, and a drive restriction control device that disables a driverestriction on the hydraulic motor by the drive restriction device whenthe working detection device detects the working state.
 15. A failuredetection device for a hydraulic motor according to claim 1, furthercomprising: a reset command switch that resets the warning device.
 16. Afailure detection device for a hydraulic motor according to claim 2,further comprising: a reset command switch that resets the driverestriction device.
 17. A failure detection device for a hydraulic motoraccording to claim 1, wherein: the warning device is reset by actuationof an ignition key switch.
 18. A failure detection device for ahydraulic motor according to claim 2, wherein: the drive restrictiondevice is reset by actuation of an ignition key switch.
 19. A hydraulicdrive vehicle, comprising: a hydraulic pump that is driven by a primemover; a hydraulic motor for traveling that is driven by hydraulic oildischarged from the hydraulic pump; an abnormality detection device thatdetects an abnormal operation of the hydraulic motor for traveling; anda warning device that issues a warning when the abnormal operation ofthe hydraulic motor for traveling is detected by the abnormalitydetection device.
 20. A hydraulic drive vehicle, comprising: a hydraulicpump that is driven by a prime mover; a hydraulic motor for travelingthat is driven by hydraulic oil discharged from the hydraulic pump; anabnormality detection device that detects an abnormal operation of thehydraulic motor for traveling; and a drive restriction device thatrestricts a driving of the hydraulic motor for traveling when theabnormal operation of the hydraulic motor for traveling is detected bythe abnormality detection device.